Certain applications may require galvanic isolation. For example, for safety reasons, AC-to-DC switch-mode power supplies typically require galvanic isolation between the AC line voltage and the outputs of the power supply. For the feedback path of the switch-mode power supply, galvanic isolation is typically accomplished by employing an opto-coupler in the signal path. Additionally, opto-couplers may be used for galvanic isolation in applications other than switch-mode power supplies.
An opto-coupler typically includes a light-emitting diode (LED) and a photodetector. A signal may be transmitted optically from the light-emitting diode to the photodetector. The light-emitting diode provides an optical signal (e.g. visible or infrared light) which, in turn, is received by the photodetector.